CuAl x Ga 1Àx Se 2 (CAGS) is an attractive wide-bandgap chalcopyrite for buffer and top cell in tandem solar cells avoiding the use of expensive In. Polycrystalline CAGS thin films with chalcopyrite structure and strongly oriented along the (112) plane have been obtained by a sequential process of vacuum evaporation and selenization, with different x values ranging from 0 to 1. The temperature of selenization has been varied between 450 and 550 8C and it has resulted on a critical parameter in the complete and homogeneous formation and crystalline quality of the CAGS thin films. The proportion of Al(x) also affects the temperature required for selenization. At least 500 8C is necessary to obtain complete formation of CAGS for x > 0.1 whereas for x 0.1 the formation takes place in a wide range of annealing temperatures. Resistivity, roughness, band gap energy, texture coefficient C 112 and crystallite size tend to increase as the selenization or annealing temperature increases. CAGS thin film properties are optimized at 525 8C for high Al proportions for which some deterioration proceeded at higher temperatures whereas at low Al proportions, a similar behaviour for 525 and 550 8C is observed.